The present invention relates to an electrostatic printing apparatus which may be used in a facsimile transmission system, electrostatic copying machine, data processing system or the like.
Such a printing apparatus generally comprises a linear array of printing electrodes which are selectively energized to apply an electrostatic charge pattern to a sheet of copy paper representing a scan line of an original document or the like. The copy sheet is incrementally moved to form a complete electrostatic image representing the entire original document. Then, a toner is applied to the copy sheet to develop the electrostatic image into a toner image which is fixed to the copy sheet to provide a permanent reproduction of the original document. Typically, one or more auxiliary electrodes are provided adjacent to the printing electrode array on either the same side or the opposite side of the copy sheet, the auxiliary electrodes being energized in a predetermined manner in combination with the printing electrodes.
Although such an apparatus is capable of high speed printing, a major problem has heretofore existed in the prior art regarding uneven printing density. This is generally due to the fact that the charge density induced on a copy sheet by a given printing electrode varies depending on the charge pattern. In other words, a particular printing electrode is influenced by the voltages applied to adjacent printing electrodes.